The invention relates to conditioning air for aircraft likely to fly at high altitude and including a cabin pressurizing system.
Such a system is fed with outside air, e.g. taken from the compressor of a turbojet. It raises the air to a pressure that is sufficient for the breathing needs of the occupants and it increases its temperature.
By way of example, an airplane flying at an altitude of 11,500 meters (m) is in an atmosphere at 206 millibars and -56.degree. C. The cabin pressurizing system raises the pressure to 810 millibars and the temperature to 22.degree. C. The humidity of air at high altitude is very low. Consequently, the relative humidity of the air injected into the cabin is well below 1%, whereas a relative humidity of 40% to 60% is desirable for the comfort of the occupants. Water vapor given off by the occupants and desorption from cabin materials are quite incapable of coming close to this value.
It might be thought that the problem could be solved by injecting vapor into the system for pressurizing and distributing air. However humidifying all of the cabin air would require a mass of water that is unacceptable for long duration flights. Also, such a system suffers from severe technical and health drawbacks. A large amount of maintenance is required and reliability is low, particularly due to piping oxidization, corrosion caused by condensation, and inorganic deposits. From the health point of view, moving humid air about the cabin and through the air conditioning pipework favors the development of bacteria, contamination by microbes, and proliferation of moss.